The Russian embassy in Washington told the BBC that it became aware of the injuries sustained by Lesin only on Thursday, when the medical examiner's report was released.

Press Secretary Yuri Melnik criticised the lack of communication by US authorities, saying Russia had made repeated requests for updates on the investigation but very few facts had been given.

Russian foreign ministry spokeswoman Maria Zakharova said Moscow expected "clarification from Washington and relevant official data on the progress of the investigation".

Competing theories

Various theories are swirling in the media about what happened to Lesin now it has it emerged that he suffered multiple injuries. Back in November Russian media, quoting his family, said he had suffered a heart attack.

Last November the UK's Daily Mail raised the possibility that the FBI could have faked Lesin's death in order to give him witness protection - as a valuable information source, since he had long been a Kremlin insider.

It also quoted Mikhail Seslavinsky, head of Russian media regulator Rospechat, as saying Lesin had appeared happy and healthy a month earlier. He added that Lesin had had complicated surgery for a spinal injury, but was now doing sports.

There are unconfirmed reports that Lesin had had a dispute with financier Yuri Kovalchuk, a longstanding friend of Mr Putin.

A Russian forensic expert quoted by Lenta.ru website (in Russian), Alexander Aulov, said Lesin's injuries were consistent with a severe beating, not an accident or the result of convulsions.

Wealth reports

In 2014, Mississippi Senator Roger Wicker called for an investigation into Lesin over possible money laundering, saying he had moved his family to the US and bought several multi-million dollar properties in California.

Sen Wicker said Lesin's fortune had raised "serious questions" and he asked how a former civil servant could have bought and maintained expensive property. He also expressed concern that the purchase might have involved people and groups on a US sanctions list.

Lesin's Gazprom-Media group is owned by Gazprombank which, in turn, has links to Bank Rossiya, described by the the EU and US authorities as "the personal bank" of top Russian officials.

Bank Rossiya is under EU-US sanctions, as is the bank's biggest shareholder Yuri Kovalchuk. He is a longstanding close aide to President Putin.

Lesin made his name in PR and advertising in the 1990s, founding advertising agency Video International or Vi - still one of Russia's biggest.

He went on to became head of the state news agency RIA Novosti and in 1996 he devised the advertising campaign that helped then President Boris Yeltsin win re-election.